Study On Influence Of Vehicle Blockage On Thermal Stratification Stability Of Tunnel Fire

The rapid development of China’s transportation has brought great challenges to the traffic.So China has built a large number of roads and railways to meet people’s demand of convenient travel and fast traffic,generating a large number of road and railway tunnels.While the tunnel provides convenient transportation and comfortable life for us,the frequency of fire accidents is also increasing.In this paper,the combination of small size experiment and FDS numerical simulation is used to study the effect of vehicle blocking effect on the thermal stratification stability of fire smoke in different situations in tunnels.In this paper,a 1:8 small-scale model test bench was built for the vehicle blocking ratio.The research was carried out with reference to 0%-50% of 6 different vehicle blocking ratios and open tunnels.The experiment found out that changing the vehicle blocking ratio has obvious influence on the thermal stratification stability of the flue gas.At 1m/s wind speed,the thermal stratification of the 50% blocking ratio is always stabler than the 0% blocking ratio.For the other four working conditions,the thermal stratification of the 30% blocking ratio is stabler than 40%,20% and 10 %,but the amplitude does not change much;at 1.5m/s wind speed,the blocking ratio change is proportional to the stratification strength,that is,the blocking ratio is increased to facilitate the stratification of the flue gas.In the stage of combustion stabilization,the greater the longitudinal wind speed,the more obvious the obstacle blocking effect is to enhance the stability of the smoke layer.In the stage of combustion decline,the blocking ratio change is inversely proportional to the stratification strength.The 40% and 50% blocking ratio is about 70% lower than the stratification strength,and the remaining working layer stratification strength is reduced in the range of 0%-50%.According to the factor of vehicle blockage length,a 150m-long tunnel was built by FDS numerical simulation,and three different fire source powers and five different lengths were set up for the research.The simulation results show that the change of vehicle length has little effect on the thermal stratification stability of smoke in different locations in the tunnel,and the main influencing factor is the fire source power.The increase of the fire source power leads to the near-fire source field and the far fire in the tunnel.The stratification stability of the flue gas in the source field has reversed.That is,the thermal stratification stability of the flue gas near the source field of the 5MW fire source power is greater than that of the far fire source field,while the thermal stratification stability of the flue gas near the source field of the20 MW source power is less than that of the far source.